DRV8840: nFAULT pulled down unexpectedly

Kevin Lin

Part Number: DRV8840

Hi there,

We are having trouble with DRV8840 whose nFAULT is pulled down unexpectedly, and only way to recover DRV8840 is to reset it. We monitor the current, temperature, and VM, and none of them ever reach the protection threshold; 1A, 35 deg C, and constant 24V, respectively. Is there any other reason the DRV8840 would enter the fault state?

Thank you

regards,

Kevin

over 6 years ago

0 Rick Duncan over 6 years ago

TI__Guru** 114905 points

Hi Kevin,

What is the sense resistor value?

Do you have a capacitor in parallel with the sense resistor.

As an experiment, please try placing a 0.1uF capacitor in parallel with the sense resistor.

0 Kevin Lin over 6 years ago in reply to Rick Duncan

Expert 1445 points

Hi Rick,

The sense resistor is 0.22ohms, and we don't have a capacitor in parallel with the sense resistor. We haven't had a chance to try adding a capacitor in parallel yet but would like to know how adding a capacitor in parallel with the sense resistor would help? Would you please give us a brief explanation? Thank you

regards,

Kevin

0 Rick Duncan over 6 years ago in reply to Kevin Lin

TI__Guru** 114905 points

Hi Kevin,

We have seen some cases where noise (negative voltage spikes) at the SENSE pin can affect operation of the device. Usually this is observed at higher currents, but it is good to rule this out.

0 Kevin Lin over 6 years ago in reply to Rick Duncan

Expert 1445 points

Hi Rick,

Unfortunately, adding a capacitor in parallel doesn't help. The nFAULT pin still got pulled down during normal operation. Is there other suggestion? Thank you

regards,
Kevin

0 Rick Duncan over 6 years ago in reply to Kevin Lin

TI__Guru** 114905 points

Hi Kevin,

Thank you for the information.

Can you provide a scope capture of the current, nFAULT voltage, and nSLEEP voltage zoomed in to show 10us prior to nFAULT asserting?

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DRV8840: nFAULT pulled down unexpectedly